Image guided medical and surgical procedures utilize patient images obtained prior to or during a medical procedure to guide a physician performing the procedure. Recent advances in imaging technology, especially in imaging technologies that produce highly-detailed, two, three, and four dimensional images, such as computed tomography (CT), magnetic resonance imaging (MRI), isocentric C-arm fluoroscopic imaging, positron emission tomography (PET), and ultrasound imaging (US) has increased the interest in image guided medical procedures.
Typically during neurological procedures, stereotactic guidance, sometimes referred to as stereotaxy, is employed by a physician to reach a target site. Stereotaxy is generally defined as the ability to locate and access an object in three-dimensional space. Stereotaxy is further characterized by surgical delivery of an instrument guided by the use of three-dimensional scanning techniques, such as computed tomography (CT) or magnetic resonance imaging (MRI). Typically, stereotaxy procedures require the use of a stereotactic head frame, which is generally referred to as a frame-based stereotaxy procedure. A typical stereotactic head frame is a halo-like device that is rigidly affixed to the patient's skull under local anesthesia, generally using four pins or screws. Once the stereotactic frame is secured, the stereotactic frame is used to define a target and a trajectory to the target, identified with the CT or MRI images. The stereotactic frame may also act as a guide for delivering various types of instruments, such as a biopsy needle or DBS leads or electrodes.
However, use of stereotactic frames may sometimes pose disadvantages. For example, to insure that the instrument guided by the stereotactic frame has reached the appropriate target, two-dimensional fluoroscopic images may be taken intra-procedurally to allow a physician to visualize the location of the instrument being advanced through the neuro structure. However, use of such fluoroscopic imaging throughout a procedure exposes both the patient and the operating room staff to radiation. Therefore, the number of fluoroscopic images taken during a procedure is preferably limited to reduce the radiation exposure to the patient and staff. Optimally, the fluoroscopic imaging would be limited to verifying that an instrument has reached the target site.
In order to adjust a stereotactic frame, the stereotactic frame typically includes various graduations or indentations that are scaled to provide separate discreet movements along the scale or vernier caliper of the stereotactic frame. Thus, the gradiations on the stereotactic frame may limit the freedom or range of motion for targeting and trajectory path of the instrument, since they may only be set between individual discreet points. Moreover, stereotactic frames may warp or bend after many years of use. This may result in inaccurate targeting and trajectories that may be unknown to a surgeon performing the procedure. Also, eliminating the graduations on the scale, eliminates motion constraints, thereby providing more precise and infinite freedom of movement for targeting and aligning instrument trajectories.
Additionally, there is generally a base of knowledge which must be acquired in order to use a conventional stereotactic frame, thereby enabling the frame to be properly positioning for the target and trajectory. In this regard, the target and trajectory adjustments are typically manually adjusted via adjustment knobs positioned on the stereotactic frame following various calculations that generally must be made in order to direct the instrument to the appropriate target. This manual adjustment of the various scales to adjust the x, y, and z coordinates, as well as the rotations about these coordinates for targeting and trajectory are susceptible to human error. Moreover, in some situations the stereotactic frame may be put in backwards or incorrectly due to human error.
An image guided surgical navigation system that enables the physician to see the location of an instrument relative to a patient's anatomy, without the need to acquire real-time fluoroscopic images throughout the surgical procedure is disclosed in U.S. Pat. No. 6,470,207, entitled “Navigational Guidance Via Computer-Assisted Fluoroscopic Imaging”, issued Oct. 22, 2002, which is hereby incorporated by reference in its entirety. In this system, representations of surgical instruments are overlaid on preacquired fluoroscopic images of the patient, based on the position of the instruments determined by a tracking sensor associated with the instruments. However, typical navigation systems generally require dynamic reference frames to track the position of the patient should patient movement occur during the procedure and also require manual registration in order to register localized preacquired images with the surgical patient space. These procedures may sometimes be time consuming and require a knowledge of surgical navigation procedures.
It is, therefore, desirable to provide a method and apparatus for performing stereotactic surgery in a more accurate and efficient manner, which does not suffer from the above-mentioned disadvantages. It is also an object of the present invention to provide such a method and apparatus for performing stereotactic surgery that provides more precise targeting and trajectory alignment, more freedom of movement, more accuracy and efficiency, automatic registration, automatic setting of the target and trajectory, reduces or eliminates the need for interoperative fluoroscopic imaging and ease of use.